Power is the product of force and velocity. Power can be expressed as an average over a range of motion or as an instantaneous value occurring at a particular instant during the displacement of an object. Peak power (PP) is the highest instantaneous value achieved during a movement. For “explosive” sports such as sprinting, jumping, and weightlifting, PP production during the activity is typically the most important variable associated with success (11, 16, 20, 30). Knowledge of the power outputs of weightlifters would therefore be useful in terms of coaching. However, measurement of power, especially PP, during weightlifting movements usually requires relatively sophisticated and expensive equipment (e.g., force plates, V-scopes, linear encoders). Most of this movement-analysis instrumentation is not typically available to most coaches. Thus, alternative methods of characterizing the power capabilities of weightlifters (or other athletes proficient in weightlifting movements) could be used.
One possible alternative would be to measure or estimate power in a mechanically related, easily measured activity. An exercise that has been observed to have mechanical similarities to weightlifting movements is the vertical jump (VJ) (4, 10). For example, average power and PP estimated from a VJ could be correlated with lifting ability (i.e., squat, snatch, and clean and jerk). This “field test” method could be carried out quickly and with relatively little interference with training (i.e., fatigue, time) and without having to perform 1 repetition maximums (1RMs) on a regular basis. The results of such field tests could provide the coach with valuable information about the potential of the weightlifter, could track fluctuations accompanying periodization of training, or could lead to alterations in the training program. However, this information must be valid and reliable to effectively aid the coach in improving athletic performance (31).
The primary purposes of this study were to correlate estimates of average power and PP derived from the VJ with performance in weightlifting movements (squat, snatch, and clean and jerk) and to determine the reliability of this method. Secondary purposes were to characterize the power output among male, female, and junior weightlifters and to determine the relationship of maximum strength (1RM squat) to the snatch and clean and jerk. Sixty-four national-level weightlifters were used to examine these associations.
Experimental Approach to the Problem
Coaches often express the need to have access to an easily administered test that will allow assessment of the athlete without actually measuring the sports performance. This study represents one approach to assessing the physical state of weightlifters that might satisfy this need. In this study, estimated power output from the VJ was correlated with lifting ability among 64 (men and women) USA national-level weightlifters.
The subjects were the men's (n = 7) and women's (n = 10) resident weightlifters at the Olympic Training Center in Colorado Springs and members of the national men's (n = 31) and women's (n = 16) junior squads. Ages ranged from 15–30 years and body mass ranged from 46.8–168.7 kg (Table 1). Junior lifters were attending 2-week training camps at the Colorado Springs Olympic Training Center, where the testing took place. This study was conducted as part of a service project in conjunction with USA Weightlifting and the U.S. Olympic Committee; all athletes (and parents of juniors) attending the U.S. Olympic Training Centers provided consent for testing as part of their participation in sports at the Olympic Training Centers.
Body mass (BdM) was measured on an electronic scale to the nearest 0.1 kg. The vertical jump was measured using the Kinematic Measurement System (Innervations, Muncie, IN), consisting of a switch mat interfaced with a laptop computer. The cost of these types of switch-mat measurement systems (without the laptop) is typically less than $500.00. This type of system was chosen over other systems that use a jump-and-reach method, as all jumps were performed with hands on hips. The hands-on-hips method was adopted in order to concentrate on leg and hip explosiveness and minimize jumping technique differences (12, 13, 31). Athletes were measured approximately 1–2 hours before lunch. In all cases jumps were measured after a light (low volume) day of training and approximately 4–5 weeks before their next competition. All athletes were familiar with the VJ and used jumping periodically in their training programs. Two types of jumps were measured, a counter-movement vertical jump (CMJ) and a static vertical jump (SJ). For the static jump the athletes were instructed to hold a knee angle of approximately 90° (by tester observation) for a count of three. Two trials were given for each condition. Test-retest reliability for jump height was intra-class correlation (ICC) = 0.98 (n = 128, CMJ) and ICC = 0.96 (n = 128, SJ). Athletes were allowed to warm-up on their own (calisthenics, jumping jacks, etc., without stretching) for 2–3 minutes, followed by 2 practice jumps at each condition (8 jumps: 2 practice and 2 measured for each jump type). Approximately 1 hour was required for 12 lifters to complete the measurements using one jump mat. Jump height was derived from flight time using the formula:
Jump height = (g × flight time × flight time)/8 Peak power was estimated using the equations developed by Sayers et al. (24):
PP (W) = (60.7) × (jump height, cm) + 45.3 × body mass - 2,055
This formula for PP estimation was chosen because (a) sex differences do not interfere with the accuracy of PP estimates, and (b) although the equation was derived from the SJ, use of the CMJ resulted in very small error (14, 24). Additionally, ICC comparisons between jumps (by assessing flight time) simultaneously measured with a force plate and the switch mat was r = 0.99 for both the CMJ and SJ.
As in most practical sports settings, actual measurement of sport performance is not always possible because it disrupts training. The athletes’ current lifting capabilities were assessed by questionnaire; each athlete was asked to report his or her current capabilities in the 1RM squat (SQ), snatch (SN), and clean and jerk (C&J). It is reasonable to assume that the listed 1RMs were valid representations because the lifters were all quite experienced and the USA national coaches and junior camp coaches checked the listed values. Previous experience with well-trained weightlifters (n = 11), in which the 1RM (SQ, SN, C&J) was actually measured and compared to estimates, showed that the estimates were within 5 kg of the actual values.
Raw data were transferred to Microsoft Excel for analyses. Peak power was calculated by entering the PP formula into the Excel spreadsheet. The following statistics were also calculated using the Excel program. Differences between groups (i.e., men versus women, junior men versus resident men, junior women versus resident women, and resident men versus resident women) were determined using t-tests with a Bonferroni adjustment (p ≤ 0.0125). Correlations were determined using Pearson's r. A correlation is the strength of the relationship among variables; the correlation coefficient (symbolized as r) ranges from -1.0 to 1.0. The further the coefficient is from zero in either direction, the stronger the relationship. A positive correlation between two variables means they increase together, and a negative correlation indicates an inverse relationship. Hopkins (15) has ranked correlations as r = 0.0 (Trivial); 0.1 (Small); 0.3 (Moderate); 0.5 (Strong); 0.7 (Very strong); 0.9 (Nearly perfect); and 1.0 (Perfect).
The mean ages and body mass measures for the lifters are shown in Table 1. Men were heavier than women, and resident men were heavier than juniors. Residents were also older than juniors. Jump heights and power outputs are shown in Table 2. Resident men had higher absolute power outputs than juniors, and men showed higher jumps and power outputs compared with women. Resident women had higher absolute power outputs than junior women. Reported weightlifting performances are shown in Table 3. As with power, residents had greater performance values than juniors, and the men performed better than the women. Selected correlations are shown in Table 4 and Table 5. These correlations indicate that maximum strength estimates (1RM squat) and PP derived from jumping are strongly related to weightlifting performance in both men and women.
PP·kg-1 values derived from jumping appear to correlate well with jumping ability. Although part of the reason for these high correlations may be related to the basic formula (24) used to predict power (i.e. [A (BdM) + B (jump height) + C]/[BdM] = A + B [jump height]/[BdM] + C/[BdM]); however, it is reasonable to assume the actual formula does accurately predict power output within a reasonable degree of error. Thus, some generalizations concerning variable relationships can be made.
This study has shown strong relationships between PP and weightlifting ability using simple methods. Furthermore, this relationship was apparent in both men and women. Importantly for the coach and athlete, PP was derived from a physical effort (VJ) that is relatively nonfatiguing and takes relatively little time to administer.
Several recent studies (5, 21, 28, 29) and a review (27) have indicated that there can be a strong association between PP and measures of explosive strength such as weighted jump squats (28), the bench press (5), arm flexion (21), and throwing performance (29). Results from the present study in which PP derived from vertical jumping correlates strongly with weightlifting performance supports this association. Indeed, if one considers the snatch and clean and jerk to be power-oriented (i.e., dynamic explosive) lifts (16, 17), then the strong relationship between the 1RM squat (maximum strength) and these lifts also supports the idea that maximum strength is strongly associated with power and explosiveness (29).
These results also indicate that body mass (BdM) strongly influences (a) estimated power production from the jumps (r = PPCMJ vs. BdM = 0.89; PPSJ vs. BdM = 0.92), (b) the 1RM squat (r = SQ vs. BdM = 0.83), and (c) the relationship between maximum strength and power calculated from the jump (r = PPCMJ vs. SQ = 0.92; PPSJ vs. SQ = 0.93). Therefore the association between absolute maximum strength and power is influenced by body mass (Table 4).
However, these results also indicate that relative measures of maximum strength influence relative measures of PP and explosiveness (ability to perform SN and C&J). For example, strong relationships between a relative measure of maximum strength (SQ·kg-1) and the SN·kg-1 (r = 0.80) and C&J·kg-1 (r = 0.85) and moderate to strong relationships between relative strength (SQ·kg-1) and relative measures of power were also observed (Table 4), indicating that maximum strength influences power independently of body mass, which agrees with previous observations (26). Similar strong correlations were noted for all groups (Table 5). Schmidtbleicher (25) indicates that maximum strength is the basic quality affecting power output; Stone et al. (27, 28, 29) also determined that maximum strength has large effects upon explosive-power-oriented sports performance. The results of the present observation support this concept.
Because lifting (SN and C&J) usually starts from a relatively static position, it may be assumed that a static vertical jump might correlate better with lifting performance (i.e., SN and C&J). However, starting from the static position may not be as important as what occurs just before and particularly during the pull. This is because the rebending of the knees in these lifts may be analogous to the countermovement in jumping. The results from this study do not indicate that one type of jump offered major advantages over the other, as both types of jump correlated strongly with the 1RM values for the weightlifting movements. Previous research indicates that the CMJ typically results in greater jump heights than the SJ (18), agreeing with the results of the present study. The CMJ is associated with a stretch-shortening cycle (SSC) that enhances performance by allowing a greater force or impulse to be reached during the concentric phase of the jump (3). The mechanism(s) by which concentric force can be augmented by a previous stretch is not completely clear but several possibilities include (a) reutilization of stored elastic energy, (b) a myototic reflex, (c) muscle-tendon interactions allowing the muscle to remain closer to its optimum length and also shorten at a more favorable velocity for force production, (d) optimizing of the muscle activation pattern, or (e) eliciting a greater preforce at initiation of the concentric phase (2, 5, 8).
Of note is the relationship between PP, PP·kg-1, the performance variables CMJ and SJ height, and the three lifts. These results suggest that for movements in which relatively light loads (no external loading) are lifted, the ability to produce high-power outputs per unit of body mass is more important than absolute power. On the other hand, when large external loads are applied (i.e., SQ, SN, C&J), absolute power production becomes a much more important factor. This observation is quite important, because it suggests that training for different types of sports would entail concentration upon developing different aspects of power production (i.e., absolute vs. relative power).
In the present study, men (n = 38) produced a 40% higher CMJ and a 30% higher SJ than the women (n = 26). The average jump-height difference between the CMJ and SJ was 5.4% for the women and 11.8% for the men. Similar results were noted for power production. These data indicate that the men were able to generate more force from the muscle's contractile apparatus (i.e., SJ differences) and were better able to utilize the SSC associated with the CMJ than the women were.
Peak power outputs for elite lifters during weightlifting movements can be greater than 52 W·kg-1 for men and 40 W·kg-1 for women (9, 11). The PP values produced during maximum lifts (9, 10, 11) are slightly lower than those produced in the jumps by the residents. Lifts of approximately 70–80% of 1RM produce the highest power outputs (about 10–20% higher than the 1RM values). If one considers jumping as “unloaded lifting,” then a continuum of PP outputs can be constructed (lifts of approximately 70% > unloaded lifts [jumps] ≥ 1RM lifts). This continuum generally fits the expected power curve generated from force-velocity relationships among highly strength-trained athletes (28). Thus, well-trained lifters would be expected to produce PP from jumps equal to or slightly higher than those observed in maximum lifts but lower than in lifts at 70–80% of maximum.
Both trained and untrained women have been shown to generate lower power outputs (both absolute and relative) compared with men (11, 19, 23). In this study the PP of the women was approximately 68% of the men and 81% for PP·kg-1. These values are similar to those obtained during the lifts of approximately 65% (absolute) and 80% (relative) (11, unpublished data).
Although, correlations between strength (1RM SQ) and jump PP values versus weightlifting ability were strong in both men and women, correlations were somewhat higher among the men. This may indicate a somewhat lesser reliance on strength and power during weightlifting movements by women (e.g., relatively greater dependence on technique factors, speed under the bar, etc.). Nevertheless, these strong correlations between the 1RM SQ, PP, and the SN and C&J indicate that among both men and women stronger more powerful athletes lift more weight.
Values for the jumps and derived PP outputs were considerably higher for the junior lifters compared with untrained adolescents of similar age (unpublished data; for review see 22). However, the older lifters (residents) produced 20–30% higher absolute PPs than the juniors but had statistically similar values for PP·kg-1. Although training differences likely play a role, part of this difference in power production may be because of differences in body mass, muscle mass, and muscle-mass distribution resulting from maturation. For example, Dore et al. (6) demonstrated that adults have a higher ratio of lean-leg volume to body mass compared to children; thus it is possible that this type of difference would be present among these groups. Several studies (1, 6, 7) have indicated that absolute short-term maximal power output measured using various protocols is lower in adolescents than in adults and that these differences can be related to differences in muscle mass and distribution. Thus, the differences in absolute power between the older and younger lifters are at least partially related to differences in body mass (muscle mass) and, perhaps, distribution.
Results indicate that vertical jump PP is strongly associated with weightlifting ability. Thus, these results indicate that PP derived from the vertical jump (CMJ or SJ) can be a valuable tool in assessing potential weightlifting performance.
The very practical approach used in this study yields data agreeing with the findings from studies that used much more sophisticated, time-consuming, and costly instrumentation. Thus, this method of evaluation could allow the coach to generally assess an athlete's “fitness” for lifting without performing 1RMs. Additionally, the method is relatively quick, results in little fatigue, and should not interfere with training.
Using simple statistical methods, associations between sports performance and jump variables can be made. Assuming that a reasonable degree of techncal skill is used in the weightlifting movements, results from the present study suggest that power derived from vertical jumps can be strongly related to weightlifting ability. Furthermore PP·kg-1 derived from the jumps is strongly related to jump height. These results suggest that, depending upon the type of sport, training should emphasize PP·kg-1 for those sports performances associated with lifting only body mass (e.g., sprinting, volleyball) and absolute power in sports in which higher external loads or forces are encountered (e.g., weightlifting, power lifting, football linemen).
Another factor for consideration is the use of this method in a weightlifting talent identification program. Because PP has been shown to have high correlations with weightlifting ability, identifying young potential weightlifters using this method would be advantageous.
Finally, it may be possible to use the PP·kg-1 or PP and jump height (provided body mass does not change substantially) as an indicator of accumulating fatigue. If marked decreases in PP·kg-1 or PP and jump height are noted this could indicate adverse adaptations to training (or total stressors) have occurred. Alternatively, alterations in power performance accompanying different phases of the periodized training program may be tracked using jump performance to assess adaptations or lack thereof which might result.
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